Flow vectorial analysis in an artificial implantable lung

An artificial implantable lung would be a useful device to support patients awaiting lung transplantation. A suitable device must offer low resistance and adequate gas exchange, be impermeable to plasma, and nonthrombogenic. Although plasma permeability is an intrinsic quality of the materials, the other requirements are largely a function of device geometry, particularly as it relates to fluid dynamics. Using a CAD system and the requirements of a membrane surface area of 1.5 m2 and an inlet outlet port distance of 12 cm, we designed 10 models that varied in their other dimensions. Computational fluid dynamic (CFD) software was applied to the models to determine which minimized regions of low flow velocity. A prototype built to these specifications was used in an in vivo ovine experiment to verify the CFD predictions. The prototype was placed in parallel to the native pulmonary circulation (pulmonary artery to left atrium) for 120 minutes while the activated coagulation times were kept between 110 and 120 seconds and device flow was maintained between 1.5 and 2.5 L/min. Examination of the prototype confirmed a correlation between predicted areas of low flow and thrombus formation. Although nearly identical low flow velocity conditions exist at both the inlet and outlet ports, thrombus formation occurs only near the outlet port. This finding agrees with detailed vectorial analysis, which predicts a more complex flow pattern near the outlet port. Although near the inlet port flow vectors are nearly parallel, near the outlet port flow vectors collide. This area of flow collision corresponds to the area of thrombus formation in vivo. The addition of microflow vectorial analysis to flow velocity predictions allows for improved accuracy in predicting regions at risk of thrombosis in an artificial implantable lung.